1. Field of the Invention
The present invention relates to the use of a novel clear coating based on organic polyisocyanates which are liquid at room temperature for the coating of sheet products based on polyvinyl chloride.
2. Description of the Prior Art
The coating of sheet products based on PVC, for example floor coverings or wall coverings of plasticized PVC, for protection against the action of chemicals or abrasion, is already known. The clear coatings hitherto used for this purpose include inter alia solvent-containing coatings in which the binders are based on polyacrylates or linear polyurethane polyureas. Owing to the generally high molecular weight of these binders, they require the use of large quantities of organic solvents. Furthermore, coatings prepared from such physically drying systems do not have sufficient resistance to organic substances which have a dissolving action. The usual two-component polyurethane coatings based on higher functional polyisocyanates and suitable hydroxy functional reactants have already been used for the coating of PVC. The advantage of these coating compounds lies in their distinctly better resistance to chemicals and solvents compared with that of the above-mentioned physically drying coating compounds, but they have the disadvantage that the addition of high proportions of organic solvents is an essential requirement as well as the disadvantage common to all two-component systems of having only a limited working time.
It has now surprisingly been found that the coating compounds according to the invention described below, consisting mainly of certain polyisocyanates which are liquid at room temperature, are eminently suitable as clear coatings for sheet products based on PVC. This observation is also surprising in view of the teaching given in German Offenlegungsschrift No. 2,845,514 since according to this prior publication the binders used for one-component systems must consist of mixtures of polyisocyanates with certain monoisocyanates and since the prior publication makes no comment on the particular suitability of the mixtures described therein for the coating of PVC.